found it, but i seem to have hard-coded the floor sizes etc.
this is the portion of the code that specifies the offsets for the tower (dungeon) data, and i have attached the BEXT binary file where you use these offsets:
Rem --- 63312 from bext
Rem --- 1358 from bextsave
Rem ---- offset -61954
BXT_MAX:
Data 7,5,8,8
BXT_SERPENT:
Data 7,5,63312
Data 17,17,63382
Data 17,17,63960
Data 17,17,64538
Data 23,23,65116
Data 19,19,66174
Data 15,15,66896
Rem -- 1088 between
BXT_CHAOS:
Data 21,21,68434
Data 21,21,69316
Data 21,21,70198
Data 21,21,71080
Data 15,15,71962
BXT_MOON:
Data 7,9,73556
Data 17,17,73682
Data 17,17,74260
Data 17,17,74838
Data 17,17,75416
Data 17,17,75994
Data 15,17,76572
Data 15,17,77082
BXT_DRAGON:
Data 21,21,78678
Data 17,17,79560
Data 15,15,80138
Data 15,15,80588
Data 12,12,81038
Data 12,12,81326
Data 12,12,81614
Data 12,12,81902
Rem -- 17x17 (578) -- 21x21 (882) -- 15x15 (450)
Rem -- 19x19 (722) -- 23x23(1058) -- 15x17 (510)